Centimeter-resolution topographic modeling and fine-scale analysis of craters and rocks at the Chang'E-4 landing site

Abstract

Chang'E-4 was the first lunar mission to successfully land on the far side of the Moon. The stereo images collected by the panoramic camera (Pancam) mounted on the Jade Rabbit-2 rover have provided the most detailed in situ observations of the landing site along the rover traverse. This paper presents our efforts in centimeter-resolution topographic modeling and fine-scale analysis of craters and rocks at the Chang'E-4 landing site using the Pancam images. We first used an integrated photogrammetric and photoclinometric approach to generate a digital elevation model (DEM) and an orthoimage mosaic of the landing site and a 3D model of the Chang'E-4 lander itself, all with spatial resolutions of 1 cm/pixel. Craters with diameters of decimeters to meters and rocks with sizes of decimeters were then extracted and analyzed. The results indicate that Chang'E-4 landed on a terrain slope of 4° toward 72.3° southwest, with one foot sunk in the regolith 1.5 cm deeper than the other foot on the front side of the lander. Fine-scale analysis of the small craters at the Chang'E-4 landing site showed overall a similar power-law trend as large craters of hundreds of meters, but there is a clear gap between their size-frequency distributions, indicating the accumulated impact flux appears to be different for these two crater populations. The average depth-to-diameter ratio of the small craters around the landing site was 0.061, obviously less than those of craters on the kilometer scale. Fine-scale analysis of rocks revealed that the Chang'E-4 landing site has a rock abundance of 0.21%, which agrees well with previous results based on orbital data. Joint analysis of craters and rocks indicates that more rocks are located inside craters with greater depth-to-diameter ratios on such a fine scale. The 3D topographic modeling approach and fine-scale analysis of craters and rocks presented in this paper provide new insights into lunar mapping and geological study.